The present invention relates to a gem grinding apparatus having a dop arm for supporting a gem at the end of a dop mounted to a collet chuck. Various rotary tools such as drills and lathes have chucks for centering a cutting tool along the axis of a tool arbor. Similarly, a collet chuck of a dop arm is used to center the dop and gem coaxially with a dop arm axis. If the chuck and dop arm are not coaxial, however, the dop cannot effectively be centered on the dop arm axis.
It is most important that the axis of the dop be in alignment with the axis of the shaft supporting it in order that the ground surfaces on the attached gem will be symmetrical. Uneven and unsymmetrical facets result if the chuck and dop are not coaxial.
The standard dop arm mounts a chuck support. The chuck support, in turn, mounts the chuck. Misalignment of the chuck axis and dop axis occurs when the chuck support is not mounted very carefully to the dop arm or becomes jarred from coaxial alignment. In present practice, the dop arm and chuck support are fitted together, using a lathe. The interfitting parts are machined simultaneously to assure a coaxial fit between the dop arm and chuck. This takes time and requires sophisticated, expensive machinery. Also, the ultimate user of the faceting machine doesn't usually have the equipment or expertise for realignment.
It becomes desirable to mount the dop support on the dop arm so it can be adjusted easily and quickly in coaxial alignment with the dop arm axis, without need for sophisticated machinery, or expertise in mechanics.